docs: def pre_filter(self):
          """ Return rTorrent condition to speed up data transfer.
          """
          if self._name in self.PRE_FILTER_FIELDS:
              val = int(self._value * self.FIELD_SCALE.get(self._name, 1))
              return '"{}=value=${},value={}"'.format(
                     self._rt_cmp, self.PRE_FILTER_FIELDS[self._name], val)
          return ''